Process of polymerization



and delayed by agitation.

a. Patented July 14,

.Charles M. Fields, Arlington, N; 1.,

E. mington, Del,

1. du Pont de Nemours 8; Company,

a corporation of Delaware assignmto Wil- No Drawing. Application July'26, 1939,

Serial No. 286,537

4 Claims.

This invention relates a process of polymerization and, more particularly, to the partial polymerization of liquid ethenoid monomers.

For the manufacture of certain synthetic resins in cast shapes, and for other purposes. it has been found advantageous to use the starting material in a partially polymerized form, rather than in a substantially monomeric form. To this end, the monomeric liquid is heated, either with or without the addition 01' a catalyst of polymerization, to a sufiiciently high temperature and for a suilicient length of time to effect a partial polymerization, whereby it is converted into a viscous syrup.

Because-the reaction-of polymerization is of exothermic nature, there is always the likelihood that it will proceed at-an undesirably rapid rate and thus, before it can be checked by chilling, carry the, polymerization further than is desired, converting the liquid to a syrup which is too viscous to be handled in subsequent operations. creases with the size of the batch in that heat developed by the reaction in the center of a large mass of liquid may not be conducted away For this reason it is esbatch which is undergoing polymerization, at a temperature which is likely to lead to loss of control, be stirred so as to prevent. local overheating.

It is an object of prove the conduct of such partial polymerization of a liquid ethenoid monomer to the form of a viscous syrup by hastening the progressof the reaction without sacrifice of the necessary control or of. the uniformity of the syrup produced. Other objects will appear from the description given hereinafter.

In accordance with the present invention, these objects are accomplished by the process comprising heating an ethenoid monomer, without or with the addition of a catalyst of polymerization and, optionally, in admixture with as fast as it develops. sential that any large plasticizers orother auxiliary ingredients, whereby to effect a partial polymerization thereof to the form of a viscous syrup and, during this period of heating, subjecting the said liquid to intermittent stirring. Preferably, the liquid undergoing polymerization is subjected alter-' nately to through agitation of brief .duration and quiescence of longer duration.

In view of the common experience that the progress of chemical reactions in a liquid phase is facilitated by view of the common practice of providingcontinuous agitation for such reaction, it is surprising that the reaction of polymerization of liquid ethenoid monomers up to the. form of a has now been found to be hindered Advantage of this discovery is talien, in the process viscous syrup Thedanger of such lack of control in-,

the present invention to km of the present periments i agitator making 42 continuous agitation, and in the development of local overheating,- particu'- larly in the center of the batch, with the resulting danger of loss of control of the real) tion.

The invention will be more apparent from the following description of carefully controlled exin which initially identical batches of monomeric methyl methacrylate were polymerized to the form of a syrup under different conditions of agitation. In each case the batch consisted of 30 pounds and the reaction was carried out in a 10 gallon container, made of stainless steel and having a jacket in which was circulated water at 82 C. No catalyst was used Agitation was effected by means of a perforated plate mounted in a horizontal plane on a vertical shaft and reciprocated vertically.

Batch A was-continuously agitated with the strokes per minute. -At the end'of 10 hours of this treatment, the methyl methacrylate had thickened only slightly. Its viscosity was measured in terms of the time required for the fall, of an aluminum ball, of diameter 0.125 inch and of specific gravity 2.7, a

Batch B was agitated only intermittently, the

agitator being alternately operated, at 42 strokes per minute, for 20 seconds and then held stationary for four minutes and'40 seconds. The agitator was thus in operation only one-fifteenth of the time. At the end of 2.75hours the viscosity of the batch was measured in the equipment just described, and at the same temperature, and found to be 700 centipoises (calculated from' falling time of 25 seconds). Throughout the reaction of polymerization to this point the odor of formaldehyde was barely detectable.

vAn analogous experiment indicates the applicability of the invention to the partial polymerization of styrene. Two-batches were processed, starting with a commonsupply of styrene, containing no catalyst. The equipment was the same as that used i theexperiment already described, jwith jacket temperature 82 C. and rate of agitation 42 strokes per minute.

Batch 1'. of styrene wasrunlike Batch A of formaldehyde, which is indicative of decomposition.

methyl methacrylate, with continuous agitation. of catalysts, the agitation is preferably both for 19 hours. Its viscosity was then about six thorough and for a relatively brief period as comcentipoises (calculated from falling time 01' Va. pared to the intervening periods of quiescence. second). The longer the periods of quiescence may be Batch II of styrene was run like Batch B of I made consistent with avoidance 01 any danger of methyl methacrylate, with intermittent agitation, local overheating and the shorter the periods of for seven hours, and reached a viscosity of 153 agitation consistent with thoroughly dissipating centipoises (calculated from falling time 5% any localities in the batch tending .to overheat, 'seconds). I Batch I was now subjected to further heating, 1o may be polymerized to a syrup or the desired under intermittent agitation, and in six hours of viscosity. this treatment reached a viscosity of 141 centi- It will be understood that the exact viscosity of poises (calculated from falling time 5 seconds). the syrup of partially polymerized material most The invention is obviously applicable primarily desirable to be obtained will vary with particular to polymerization in batches of commercial size, 15, s to w h the syrup is to be p nd th t th for whi h it will ordinarily be desirable to prodetermination of the particular viscosity forms vide power-driven agitators. In such equipment. no part of the present invention. th desired intermittent operation of the agitator An advantage of the process of the present incan'be efiected automatically by a suitable clockvention is that it promotes to an extraordinary controlled switch. In the absence of such mezo-degree the rapid partial polymerization of ethechanical equipment, the procedure of .the invennoid monomers to the o d n of vis us syrup tion can be carried out by intermittently stirring while preventing loss of cont 1 of the exothermic the contents of a container by other means. reaction of polymeriza ion an minimizing No agitation at all need be given during the composition or the ethenoid monomers.

first stages 01' the reaction, corresponding to what s any a a y w d y d nt m dihas been called the incubation period, during ments of this invention may be made without dewhich period no appreciable increase of viscosit part f m e s it and s ope the e it is is observed. Once the viscosity has begun to .into be understood that the invention is not limited crease. indicating the initiation or active polyi t e specific em dimen s ereo e pt s merization, the agitationis to be provided merely define in the appended claims. at intervals closely enough spaced to avoid the 11 risk of los'sof control through local overheating 1. A process of partially polymerizing, in relamade possible-by lack ofagitation. The intervals tively a e ch s. m nomeric methyl methaof time between successive brief periods of agitacrylate t0 Y us Syrup Which mp s heaton 111 thus b horter the higher the tempera 3t; ing said methyl methacrylate in the absence of a ture at which thebatch is being held, and more uid v i le and, during sa d h a at east the more rapidly and efiiciently the monomer frequent agitation will'be needed if catalyst is after the increase in viscosity of said liquid com-- present than. if it is not. .The quality or' the menace, subjecting sa d methyl m tha y ate t monomeric substance al ha a b ari upon th periods oi agitation of about 20 seconds duration facility with which polymerization proceeds. at about mi e in e va s.

A typical routine under the process of the-in- 2. A process of partially po yme i n relavention may be seen in the polymerization of a tively large batches, monomeric styrene to a visbatch or aoo pounds of methyl methacrylate, coils y up whi h comprises heating a d styrene without catalyst, in a vessel 01' aluminum of so in the a sence ofa li ui vehicle and, durin gallons capacity, with heat supplied-by a water said heating at least after the increase in visjacket maintained t 79 c, Agitation is supcosity of said liquid commences, subjecting said plied for periods oi 20 seconds at interval of styrene to periods of agitation of about 20 secfive minutes. Polymerization roc d smoothly onds duration at about 5 minute intervals.

and under control, with very little evolution 01' Ap c sa of pa tia y p ym n n elaformaldehyde, and the syrup discharged from the 4' hatches. a liq id polymerizable monovessel when the proper viscosityhasbeenreached from the '0"? ("insisting of styrene and is uniform in viscosity. In ab t 3,5 hem-s 1 the saturated aliphatic alcohol esters of methacosity or 700 cent1po is reached, crylic acid, to a viscous syrup which comprises In th early stages, ggitgflon t longer t heating said monomer in the absence of a liquid vals would sumce, but it is more convenient and Ivehlcle n during said heating at least after perfectly satisfactory, particularly if automati the increase in viscosity of said liquid commeans or control are used, to start with agitation a. u jecting said m n m r a nat ly t at th some i t r as will be desirable toward periods of agitation and quiescence, the duration the end of. the reaction, when the danger or loss 0f said Periods of agiiativn being about In of of control is mare meat the duration oi said periods of quiescence and b appamnt t those skilled in t n the periods of quiescence being of insumcient the proce s or the present invention is roadly duration to P i local v at n of the polyapplicable to liquid ethenoid monomers. Qmong 11161111118 -V such monomers are acrylic and methacrylic acids A Pmcess Partially m rizin in rei s- I i an heir numerous derivatives as the tinn tively large batches, aliquid-polymerizable monodrides, amides, nitriles, esters, and the like, vinyl from the group consisting o s yrene and hali es and esters, and styren Obviously, the he saturated aliphatic alcohol esters of methapresent process is applicableto mixture of monocrylic a d. to a viscous syrup which comprises mer adapted to produce interpolymers as well heating said monomer in the absence of a liquid assingle monomers, vehicle and during said 11 tin t i ea g a least after 0 the ptimum timing of the periods of the increase in viscosity of said liquid comagitation and ce aocordingtothe present mences. subjecting said monomer to i periods of inventionis bound to vary with diiterent monomoti n of about twenty seconds durati t mars, the temperature of polymerization, the about five-minute intervals. on a volume 01' monomer, andfthe presence or absence I CHARLES M. FIELDS- a f I I I 

